Dynamic statistical parametric mapping: Combining fMRI and MEG for high-resolution imaging of cortical activity

Functional magnetic resonance imaging (fMRI) can provide maps of brain acti vation with millimeter spatial resolution but is limited in its temporal re solution to the order of seconds. Here, we describe a technique that combin es structural and functional MRI with magnetoencephalography (MEG) to obtai n spatiotemporal maps of human brain activity with millisecond temporal res olution. This new technique was used to obtain dynamic statistical parametr ic maps of cortical activity during semantic processing of visually present ed words. An initial wave of activity was found to spread rapidly from occi pital visual cortex to temporal, parietal, and frontal areas within 185 ms, with a high degree of temporal overlap between different areas. Repetition effects were observed in many of the same areas following this initial wav e of activation, providing evidence for the involvement of feedback mechani sms in repetition priming.